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General Introduction
********************

This file documents 'awk', a program that you can use to select
particular records in a file and perform operations upon them.

   Copyright (C) 1989, 1991, 1992, 1993, 1996-2005, 2007, 2009-2022
Free Software Foundation, Inc.


   This is Edition 5.2 of 'GAWK: Effective AWK Programming: A User's
Guide for GNU Awk', for the 5.2.1 (or later) version of the GNU
implementation of AWK.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License", with the
Front-Cover Texts being "A GNU Manual", and with the Back-Cover Texts as
in (a) below.  A copy of the license is included in the section entitled
"GNU Free Documentation License".

  a. The FSF's Back-Cover Text is: "You have the freedom to copy and
     modify this GNU manual."

* Menu:

* Foreword3::                      Some nice words about this
                                   Info file.
* Foreword4::                      More nice words.
* Preface::                        What this Info file is about; brief
                                   history and acknowledgments.
* Getting Started::                A basic introduction to using
                                   'awk'. How to run an 'awk'
                                   program. Command-line syntax.
* Invoking Gawk::                  How to run 'gawk'.
* Regexp::                         All about matching things using regular
                                   expressions.
* Reading Files::                  How to read files and manipulate fields.
* Printing::                       How to print using 'awk'. Describes
                                   the 'print' and 'printf'
                                   statements. Also describes redirection of
                                   output.
* Expressions::                    Expressions are the basic building blocks
                                   of statements.
* Patterns and Actions::           Overviews of patterns and actions.
* Arrays::                         The description and use of arrays. Also
                                   includes array-oriented control statements.
* Functions::                      Built-in and user-defined functions.
* Library Functions::              A Library of 'awk' Functions.
* Sample Programs::                Many 'awk' programs with complete
                                   explanations.
* Advanced Features::              Stuff for advanced users, specific to
                                   'gawk'.
* Internationalization::           Getting 'gawk' to speak your
                                   language.
* Debugger::                       The 'gawk' debugger.
* Namespaces::                     How namespaces work in 'gawk'.
* Arbitrary Precision Arithmetic:: Arbitrary precision arithmetic with
                                   'gawk'.
* Dynamic Extensions::             Adding new built-in functions to
                                   'gawk'.
* Language History::               The evolution of the 'awk'
                                   language.
* Installation::                   Installing 'gawk' under various
                                   operating systems.
* Notes::                          Notes about adding things to 'gawk'
                                   and possible future work.
* Basic Concepts::                 A very quick introduction to programming
                                   concepts.
* Glossary::                       An explanation of some unfamiliar terms.
* Copying::                        Your right to copy and distribute
                                   'gawk'.
* GNU Free Documentation License:: The license for this Info file.
* Index::                          Concept and Variable Index.

* History::                             The history of 'gawk' and
                                        'awk'.
* Names::                               What name to use to find
                                        'awk'.
* This Manual::                         Using this Info file. Includes
                                        sample input files that you can use.
* Conventions::                         Typographical Conventions.
* Manual History::                      Brief history of the GNU project and
                                        this Info file.
* How To Contribute::                   Helping to save the world.
* Acknowledgments::                     Acknowledgments.
* Running gawk::                        How to run 'gawk' programs;
                                        includes command-line syntax.
* One-shot::                            Running a short throwaway
                                        'awk' program.
* Read Terminal::                       Using no input files (input from the
                                        keyboard instead).
* Long::                                Putting permanent 'awk'
                                        programs in files.
* Executable Scripts::                  Making self-contained 'awk'
                                        programs.
* Comments::                            Adding documentation to 'gawk'
                                        programs.
* Quoting::                             More discussion of shell quoting
                                        issues.
* DOS Quoting::                         Quoting in Windows Batch Files.
* Sample Data Files::                   Sample data files for use in the
                                        'awk' programs illustrated in
                                        this Info file.
* Very Simple::                         A very simple example.
* Two Rules::                           A less simple one-line example using
                                        two rules.
* More Complex::                        A more complex example.
* Statements/Lines::                    Subdividing or combining statements
                                        into lines.
* Other Features::                      Other Features of 'awk'.
* When::                                When to use 'gawk' and when to
                                        use other things.
* Intro Summary::                       Summary of the introduction.
* Command Line::                        How to run 'awk'.
* Options::                             Command-line options and their
                                        meanings.
* Other Arguments::                     Input file names and variable
                                        assignments.
* Naming Standard Input::               How to specify standard input with
                                        other files.
* Environment Variables::               The environment variables
                                        'gawk' uses.
* AWKPATH Variable::                    Searching directories for
                                        'awk' programs.
* AWKLIBPATH Variable::                 Searching directories for
                                        'awk' shared libraries.
* Other Environment Variables::         The environment variables.
* Exit Status::                         'gawk''s exit status.
* Include Files::                       Including other files into your
                                        program.
* Loading Shared Libraries::            Loading shared libraries into your
                                        program.
* Obsolete::                            Obsolete Options and/or features.
* Undocumented::                        Undocumented Options and Features.
* Invoking Summary::                    Invocation summary.
* Regexp Usage::                        How to Use Regular Expressions.
* Escape Sequences::                    How to write nonprinting characters.
* Regexp Operators::                    Regular Expression Operators.
* Regexp Operator Details::             The actual details.
* Interval Expressions::                Notes on interval expressions.
* Bracket Expressions::                 What can go between '[...]'.
* Leftmost Longest::                    How much text matches.
* Computed Regexps::                    Using Dynamic Regexps.
* GNU Regexp Operators::                Operators specific to GNU software.
* Case-sensitivity::                    How to do case-insensitive matching.
* Regexp Summary::                      Regular expressions summary.
* Records::                             Controlling how data is split into
                                        records.
* awk split records::                   How standard 'awk' splits
                                        records.
* gawk split records::                  How 'gawk' splits records.
* Fields::                              An introduction to fields.
* Nonconstant Fields::                  Nonconstant Field Numbers.
* Changing Fields::                     Changing the Contents of a Field.
* Field Separators::                    The field separator and how to change
                                        it.
* Default Field Splitting::             How fields are normally separated.
* Regexp Field Splitting::              Using regexps as the field separator.
* Single Character Fields::             Making each character a separate
                                        field.
* Command Line Field Separator::        Setting 'FS' from the command
                                        line.
* Full Line Fields::                    Making the full line be a single
                                        field.
* Field Splitting Summary::             Some final points and a summary table.
* Constant Size::                       Reading constant width data.
* Fixed width data::                    Processing fixed-width data.
* Skipping intervening::                Skipping intervening fields.
* Allowing trailing data::              Capturing optional trailing data.
* Fields with fixed data::              Field values with fixed-width data.
* Splitting By Content::                Defining Fields By Content
* More CSV::                            More on CSV files.
* FS versus FPAT::                      A subtle difference.
* Testing field creation::              Checking how 'gawk' is
                                        splitting records.
* Multiple Line::                       Reading multiline records.
* Getline::                             Reading files under explicit program
                                        control using the 'getline'
                                        function.
* Plain Getline::                       Using 'getline' with no
                                        arguments.
* Getline/Variable::                    Using 'getline' into a variable.